An implantable retina with multilayer optical filters converts near-infrared light into neural signals. It restores and extends vision without affecting natural sight, offering new possibilities for visual prosthetics.
Study: An implantable epiretinal device for near-infrared light perception. Image Credit: Elnur/Shutterstock
In a recent article published in the journal Nature Electronics, researchers introduced an innovative implantable artificial retina capable of converting near-infrared (NIR) light into electrical stimuli that directly activate retinal neurons. This device aims to extend the mammalian visual spectrum into the NIR domain without impairing existing visible-light vision.
Limitations of Natural Vision and the Potential of NIR-Based Prosthetics
Visual perception in mammals is primarily mediated by photoreceptor cells in the retina that detect visible light wavelengths ranging from 400 to 700 nm. However, diseases causing degeneration of these photoreceptors lead to blindness, removing this critical sensory input. Near-infrared (NIR) light, which lies beyond the visible spectrum (above 700 nm), offers a promising alternative spectral range for visual prosthetics. Still, mammalian photoreceptors are naturally insensitive to it due to high thermal noise and low photon energy.
Existing retinal prostheses primarily focus on restoring perception within the visible spectrum by electrically stimulating inner retinal layers such as retinal ganglion cells (RGCs). Integration of optoelectronics with biological systems has enabled new methods of vision restoration and enhancement, including augmenting natural capabilities with NIR detection. Creating a device that reliably and selectively detects NIR light while allowing visible light to pass through requires sophisticated optical filtering techniques.
Design of a Dual-Mode Optical Interface for Visible and NIR Light
The central optical innovation involves constructing an ultrathin (360 nm) NIR-transmission filter, patterned by photolithography, above an array of single-crystalline silicon phototransistors. This filter consists of amorphous silicon (a-Si) and silicon dioxide (SiO2) layers arranged to selectively transmit NIR light while blocking visible wavelengths.
Visible light reaches the retina by passing through gaps in the filter pattern, activating remaining natural photoreceptors. Meanwhile, NIR light penetrates the filter, stimulating the phototransistor array beneath. The device's phototransistors amplify NIR-induced photocurrents, which are then delivered as electrical stimuli through 3D liquid metal micropillar electrodes to the RGC layer.
These liquid metal electrodes,via 3D liquid-metal composed mainly of eutectic gallium indium (EGaIn), are fabricated via direct printing and coated with a thin parylene C film, leaving only the tips exposed and functionalized with platinum nanoclusters to reduce impedance. Their soft, pillar-shaped structure provides closer, more efficient electrical coupling with retinal neurons than flat electrodes, enabling more effective stimulation with minimal tissue trauma.
To improve real-world functionality, a multilayer optical filtering system was developed, comprising alternating layers of Silicon oxide and a-Si. This multilayer design allows tuning of the filter’s central wavelength and bandwidth, and also provides angle selectivity to reduce interference from off-angle or background NIR light, such as solar radiation and artificial sources.
Device Performance: Sensitivity, Uniformity, and Signal Amplification
The NIR-transmission filter demonstrated precise optical properties, selectively passing near-infrared wavelengths while effectively blocking visible light. Scanning electron microscopy confirmed the fine structure and patterning integrity of the filter. Electrophysiological tests in vitro and ex vivo validated the phototransistor array’s high sensitivity and transistor characteristics under NIR illumination. The devices showed excellent uniformity and high on/off ratios, critical for effective photodetection and neural stimulation.
Biocompatibility assays supported the safety of the filter and electrode materials, with human retinal pigment epithelium cells maintaining high viability when cultured on the device, and no evidence of inflammation or tissue damage was found six months post-implantation in healthy mice.
Behavioral and neural activity studies in live mice highlighted functional success. Mice implanted with the device exhibited cortical neural responses to NIR light stimuli that were absent in control groups, confirming that the optical and electrical system effectively extended visual detection into the NIR spectrum. The overlay of the NIR filter did not impair normal visible-light perception, enabling simultaneous dual-modality vision. This coexistence was attributed to the precise spatial and spectral selectivity offered by the patterned filter design.
The multilayer optical filters provided enhanced selectivity by narrowing the NIR bandwidth and offering angular discrimination. Filters tuned to different central wavelengths (950 nm, 1000 nm, 1050 nm) demonstrated that spectral tuning is achievable through careful layer design. Furthermore, angle-selective filters reduced background NIR noise by limiting transmission to near-normal incidence angles, crucial for practical applications in variable lighting conditions.
Collectively, the optical filtering architecture and phototransistor design form a robust optical-electrical interface that can be tailored to different spectral targets through material and structural modifications. The flexible implantable retina also integrates innovations from optics and bioelectronics, improving both the quality and specificity of stimulation for vision restoration or augmentation.
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Implications for Vision Restoration and Sensory Augmentation
This study presents a pioneering epiretinal implant that selectively detects near-infrared light through an ultrathin, multilayered transmission filter integrated atop a silicon phototransistor array. This optical engineering breakthrough offers promising avenues for vision restoration therapies, where multifaceted optical filtering enables nuanced control over spectral sensitivity, precision targeting of retinal neurons, and coexistence with remaining natural visual functions.
Journal Reference
Chung W.G., Jeong I., et al. (2026). An implantable epiretinal device for near-infrared light perception. Nature Electronics. DOI: 10.1038/s41928-026-01601-8, https://www.nature.com/articles/s41928-026-01601-8